Wave length modulating device



Patented Feb. 14, 1950 WAVE LENGTH MODULATING DEVICE Gerard Hepp,Eindhoven, Netherlands, assignor to Hartford National Bank & TrustCompany, Hartford, Conn., as trustee Application May 13, 1947, SerialNo. 747,778 In the Netherlands May 23, 1946 Claims.

1 The invention relates to a device for producing oscillations modulatedin frequency or in phase by sound oscillations, more particularly forbeing used as a communication transmitter. In transmitters of this kindthe carrier frequency must be very constant, whereas the frequency sweepis allowed to be comparatively small, since the frequency range occupiedby the communication to be transmitted is comparatively small.

The'object of this invention is to provide a means to frequencyorphase-modulate a given constant oscillator frequency in accordance withsome desired transverse audio wave. According to the invention, thismodulation may be made to vary in a predetermined manner as a functionof the frequency of the impinging transverse audio wave by amanipulation of the physical properties of certain circuit elements.

In a well-known circuit-arrangement phase modulation is effected bysupplying a carrier oscillation of constant frequency, for example,originating from a crystal-controlled oscillator, to a phase-displacingnetwork, in which the phase displacement depends on a modulatingquantity, for example, a modulating current, which varies the inductanceof coils included in the network, the phase-shifting being subsequentlymaterially increased with the aid of frequency multipliers.

According to the invention, phase displacement is effected by includingreactances in the phase-displacing network, which are mechanicallyvaried by sound oscillations.

It is known per se to include reactances varied by sound oscillations inthe tuning circuit of a generator of frequency-modulated oscillationsbut such a generator exhibits the limitation in that the centralfrequency is not constant.

To constitute variable reactances use may be made in particular ofcondensers; these variable condensers can readily be united to form asingle condenser microphone by dividing one of the electrodes of such amicrophone into a plurality of relatively insulated sectors.

In order that the invention may be more clearly understood and readilycarried into effect, it will now be explained more fully with referenceto the accompanying drawing.

Figure 1 illustrates one embodiment of the invention;

2 which produces the oscillation to be modulated and 2 a phase-shiftingnetwork, in which the capacities C are each constituted by the capacityof each sector of the subdivided electrode of a condenser microphonerelatively to the other nonsubdivided electrode.

By suitable choice of the mechanical constants the characteristic curveof the microphone may be given such form that the low notes of the soundoscillations to be transmitted bring about a materially larger capacityvariation than the high notes. This device produces frequencymodulatedoscillations, while dispensing with the customary integrating networkwhich is otherwise essential to produce frequency-modulated oscillationswith the aid of phase-modulators and transforms the modulating soundoscillations in such manner thatthe modulated oscillation exhibits afrequency deflection which is proportional to the sound oscillations. Ingeneral, however, the characteristic curve of the microphone will begiven a considerably less marked form than corresponds with completeintegration in order to ensure at the same time the preemphasis of thehigh notes.

Fig. 2 illustrates the frequency characteristic curve of a microphone ofthis kind.

Fig. 3 shows a cross-section of the variable reactance elements referredto in Fig. 1. Each of the reactive components marked C are shown withexternal leads on one side and a common plate or diaphragm on the otherforming both the electrical terminal and the diaphragm upon which thesound oscillations impinge. Such impinging will cause a relativedisplacement of the diaphragm and, therefore, the reactance between thecommon terminal and the individual lower terminals will vary as afunction of the sound oscillation.

The frequencyor phase-modulated oscillations set up in the outputcircuit of the phase-shifting network 2 may be fed, as indicated in Fig.l, to a frequency multiplier 3 in order to increase the frequency orphase deflection.

What I claim is:

1. A wavelength modulating circuit arrangement; comprising a source ofoscillatory potential, an output circuit coupled to said source andmeans to vary the phase of said potential, said means comprising anelectro-acoustical capacitative transducer responsive to sound wavesimpinging thereon and having a first electrode and a second electrodecomprising a plurality of electrode elements} in capacitativerelationship with said first electrode and defining a plurality ofdistinct capacitors with said first electrode, one of said electrodesbeing in the form of an acoustically vibratory diaphragm and thecapacity of each of said capacitors being individually variable inproportion to the magnitude of the sound waves impinging on saiddiaphragm, an impedance element interconnecting two of said secondelectrode elements to form therewith and with said first electrode aphase shifting network, and means to connect said network to said sourceto vary the phase of said source in proportion to the magnitude of thesound waves impinging on said dia phragm.

2. A wavelength modulating circuit arrangement, comprising a source ofoscillatory potential, an output circuit coupled to said source andmeans to vary the phase of said potential, said means comprising anelectro-acoustical capacitative transducer responsive to sound wavesimmeans to connect said network to said source to vary the phase of saidsource as a function of the magnitude of the sound waves impinging onsaid diaphragm.

3. A wavelength modulating circuit arrangement, comprising a source ofoscillator potential, an output circuit coupled to said source and meansto vary the phase of said potential, said means comprising anelectro-acoustical capacitative transducer responsive to sound wavesimpinging thereon including an acoustically vibratory conductivediaphragm, a plurality of electrodes, each electrode in conjunction withsaid diaphragm defining a distinct capacitor, the capacity of each ofsaid capacitors being variable in magnitude in proportion to themagnitude and in inverse proportion to the frequency of soundoscillations impinging on said diaphragm, a plurality of impedanceelements interconnecting said electrodes to form therewith a phaseshifting network, and means to connect said network to said source tovary the phase of said source in proportion to the magnitude and ininverse propor-- tion to the frequency of the sound waves impinging onsaid diaphragm.

'4. A wavelength modulating circuit arrangement, comprising a source ofoscillatory potential,

an output circuit coupled to said source and .an electro-acousticalcapacitative transducer responsive to sound waves inpinging thereon fortranslating sound energy into electrical energ and for coupling saidsource of oscillator potential to said output circuit including a firstelectrode and a second electrode comprising a plurality of electrodeelements in capacitative relationship with said first electrode anddefining a plurality of distinct capacitors with said first electrode,one of said electrodes being in the form of an acoustically vibratorydiaphragm and the capacity of each of said capacitors being individuallyvariable in proportion to the magnitude of the sound waves impinging onsaid diaghrag-m, an impedance element interconnecting two of said secondelectrode elements to form therewith and with said first electrode aphase shifting network, and means to connect said network to said sourceto vary the phase of the source in proportion to the magnitude of thesound waves impinging on said diaphragm.

5. A wavelength modulating circuit arrangement, comprising a source ofoscillatory potential, an output circuit coupled to said source and anelectro-acoustical capacitative transducer responsive to sound wavesimpinging thereon for translating sound energy into electrical energyand for coupling said source of oscillatory potential to said outputcircuit including an acoustically vibratory conductive diaphragm, aplurality of electrodes, each electrode in conjunction with saiddiaphragm defining a distinct capacitor, the capacity of each of saidcapacitors being variable in magnitude as a, function of the magnitudeof sound oscillations impinging on said diaphragm, a plurality ofimpedance elements interconnecting said electrodes to form therewith andwith said diaphragm a phase shifting network and means to connect saidnetwork to said source to vary the phase of said source as a function ofthe magnitude of the sound waves impinging on said diaphragm.

GERARD HEPP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,615,645 Nyman Jan. 25, 19272,077,223 Crosby Apr. 13, 1937 2,262,468 Percival Nov. 11, 19412,418,842 Kinsburg Apr. 15, 1947

